1. Field of the Invention
The present invention relates to a mowing apparatus with two oscillatable cutting members.
2. Description of the Prior Art
One example of an oscillative mowing apparatus is illustrated in European Patent Application No. 87112105.9 filed by the applicant of the present invention. First and second superposed cutting disks are used in the mowing apparatus of that patent application. The two cutting disks oscillate in opposite directions within a predetermined oscillating range, through a crank mechanism. Specifically, as shown in FIGS. 1 and 2, a tubular first shaft 3 is integrally provided at the center of a first cutting disk 1U. The first shaft 3 is rotatably provided in a casing 5 through a bearing. Also, a second shaft 7 is integrally provided at the center of a second cutting disk 1L, and the second shaft 7 is rotatably inserted into the first shaft 3 in the axial direction. The bases of a first arm 9U and a second arm 9L are integrally mounted on the first and second shafts 3, 7 respectively. The tip of the first arm 9U is connected to a first link 11U and the tip of the second arm 9L is connected to a second link 11L. A cam shaft 13 provided with two circular eccentric cams 15U, 15L is installed in the casing 5. The first and second links 11U, 11L are slidably fitted into the circular eccentric cams 15U, 15L, respectively. The cam shaft 13 is connected to a motive power source through a large gear 17, a small gear 19, an intermediate shaft 21, a bevel gear 23, a bevel gear 25, and a drive shaft 27.
In the above structure, the rotational motion of the motive power source is transmitted to the cam shaft 13, causing the cam shaft 13 to rotate. The two eccentric cams 15U, 15L rotate as a result of the rotational motion of the cam shaft 13, and the first and second arms 9U, 9L are reciprocatingly pivoted in opposite directions through the first and second links 11U, 11L. Then, the first and second cutting disks 1U, 1L oscillate reciprocatingly in opposite directions through the pivoting action of the arms 9U, 9L, thereby enabling to cut grass between the teeth of the upper and lower cutting disks as scissors.
The conventional mowing apparatus described above is highly superior in safety of operation. However, in the conventional mowing apparatus, the relative positional relationship of the teeth of the upper and lower cutting disks during the oscillating action of the cutting disks of this mowing apparatus, as indicated by the solid line "A" in FIG. 3, is represented in the form of a sine curve. Specifically, in the conventional mowing apparatus, the upper teeth 29U move relatively from one superposed state in which the upper teeth 29U are superposed on the lower teeth 29L (this state corresponds to the top or the bottom of the sine curve) to the next superposed state in which the upper teeth 29U are superposed on the adjacent lower teeth 29L (this state corresponds to the bottom or the top of the sine curve). Then the upper teeth 29U move in the reverse direction toward the first superposed state and are once again superposed on the previous lower teeth 29L. At this time, the motion of the upper and lower teeth 29U, 29L, slows down according as the superposed position (the top or the bottom of the sine curve) is approached, and the moving speed becomes highest when the upper and lower teeth are in alternate positions (this state corresponds to the middle portion of the sine curve). In this case, it is apparent that slope of the curve represents moving speed of the cutting teeth. Therefore, in the conventional mowing apparatus, the moving speed of the cutting teeth when the upper teeth 29U are superposed on the lower teeth 29L becomes extremely low. Grass is being cut by the teeth just before the superposed states. This means that the grass is being cut by the relatively low moving speed of the cutting teeth.
Accordingly, in the conventional mowing apparatus, there is a problem that the highest moving speed of the cutting teeth could not be used in the grass cutting operation. Further, because the moving speed of the cutting teeth is slow before and after the teeth reach the superposed position and there is no stationary state when the teeth of the upper and lower cutting disks are superposed, the duration of the period when the upper and lower teeth 29U, 29L are fully superposed (this state corresponding to the top or bottom of the sine curve) is short. For this reason, only a short time is available to the cutting disks in the condition where there is a wide space between each of the teeth 29U and each of the teeth 29L, which is necessary to receive the grass to be cut between the teeth as much as possible.